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Multilevel and Continuous Pleural Fluid pH Likelihood Ratios for Evaluating Malignant Pleural Effusions^*

^* From the Division of Pulmonary and Critical Care Medicine (Dr. Heffner), Medical University of South Carolina, Charleston, NC; School of Law (Mr. Heffner), University of Texas, Austin, TX; and Lovelace Health Systems and the University of New Mexico School of Medicine (Dr. Brown), Albuquerque, NM.

Correspondence to: John E. Heffner, MD, FCCP, Medical University of South Carolina, Division of Pulmonary and Critical Care Medicine – 812 CSB, 96 Jonathan Lucas St, PO Box 250623, Charleston, SC 29425; e-mail: heffnerj{at}musc.edu

Study objective: Expert consensus recommends testing pleural fluid for pH to assist the selection of patients with malignant pleural effusions for pleurodesis. Although published studies report an association between pleural fluid pH and patient outcomes after pleurodesis, clinicians have no definitive information on how to use pH to select patients for pleurodesis. Thus, we quantitatively assessed different methods for deriving likelihood ratios from pleural fluid pH and evaluated the potential role of pH in selecting patients for pleurodesis.

Data sources: MEDLINE, systematic reviews, article reference lists, and contact with primary authors.

Study selection: Studies that assessed the impact of pleural fluid pH on survival and pleurodesis failure rates among patients with malignant pleural effusions.

Data extraction: Primary authors provided their data in electronic spreadsheets.

Data synthesis: Retrieved data sets included survival and pleurodesis failure rates for 417 patients and 433 patients, respectively. Binary, multilevel, and continuous likelihood ratios were calculated to estimate the likelihood of death within 3 months of pleurodesis or pleurodesis failure rates. Values for the likelihood ratios were compared for each of the three strategies, and relative clinical and statistical significance were assessed. Pleural fluid pH had marginal performance for identifying patients with < 3-month anticipated survival; binary likelihood ratios provided as much information as the multilevel and continuous strategies. Likelihood ratios for identifying patients likely to fail pleurodesis were clinically useful. Continuous likelihood ratios provided statistically more information as compared with the multilevel and binary strategies.

Conclusions: Pleural fluid pH has marginal value for estimating death within 3 months of pleurodesis, and binary likelihood ratios (cut point ≤ 7.20) perform as well as the other strategies assessed. Pleural fluid pH provides more useful information for estimating the likelihood of pleurodesis failure for which continuous likelihood ratios provide the most information as compared with binary or multilevel likelihood ratios.

Key Words: diagnostic testing • malignant • pH • pleura • pleural effusions